tail, it suffered tail vibration at certain power settings which resulted in the addition of tail-bracing struts. It was officially tested during July–December 1934, but was not accepted for service by the Soviet Air Force, as it now wanted fighters armed with heavy recoilless rifles, and interest switched to the Tupolev ANT-29 derivative. Specifications (ANT-21D) Notes References Duffy, Paul and Andrei Kandalov. Tupolev The Man and His Aircraft. Shrewsbury, UK:Airlife Publishing, 1996. . Green, William and Gordon Swanborough. The Complete Book of Fighters. New York, Smithmark, 1994. . Gunston, Bill. The Osprey Encyclopedia of Russian Aircraft 1875–1995. London:Osprey, 1995. . 1930s Soviet fighter aircraft ANT-21 Aircraft first flown in 1933 Low-wing aircraft Twin piston-engined tractor aircraft